1. Field of the Invention
The present invention relates generally to power steering pumps and more specifically to a power steering pump having a cover plate containing pump vane porting.
2. Description of Related Art
A power steering system used with an automotive vehicle typically utilizes a power steering pump that provides hydraulic fluid under pressure to a power steering gear assembly. The pump includes a cam plate having a cam chamber. A rotor, mounted for rotation on a shaft journaled in the housing, is located in the cam chamber. The rotor includes retractable or moveable vanes that move radially in and out depending on their location or position in the cam chamber. The cam plate is disposed between upper and lower pressure plates and located within a housing of the pump. A cover plate secures the cam plate, rotor and pressure plates within the housing.
During operation, the vehicle engine, using a belt and pulley mechanism connected to shaft journaled in the housing drives the rotor. As the rotor turns, the vanes operate to compress and discharge the pressurized fluid through fluid passageways to the outlet port and ultimately to the power steering gear assembly. At least one fluid inlet port supplies fluid to the cam chamber.
The upper pressure plate located between the cover and cam plate typically has porting or passageways that route the power steering fluid. Accordingly, the upper pressure plate cooperates with the cover to route or provide high-pressure fluid from the outlet port through under vane porting on the upper pressure plate to correspondingly distribute fluid into the cavities underneath the vanes to drive the vanes out at certain locations or positions in the cam chamber. The upper pressure plate also has porting that relieves or enables the pressure to escape and allow the vanes to retract of extend radially inward as they travel within the cam chamber.
In addition, sealing the assembly within the housing, the cover plate may include an aperture or bore that supports the shaft bushing. Accordingly, rotation of the rotor provides pressurized fluid to the fluid output port and to the cam chamber to move the rotor vanes. Due to the intricacy of the fluid ports and passageways, the cam plate and pressure plates must be accurately aligned with respect to one another in the housing whereby the cam chamber is properly aligned with the inlets and outlets to ensure proper pressure flow. To ensure a proper fit and seal it is necessary to grind the two side surfaces of the upper pressure plate and the surface of the cover. This process increases the cost of the pump and provides an additional leak path.
Therefore there exists a need for a power steering pump that utilizes a single component that combines the upper pressure plate and cover into a single piece that includes the fluid inlet and outlet porting along with the under vane porting. Such a pump reduces the number of components and potential leak paths.